libvirt users - Jan 2018 - Whether libvirt can support all backing chain layer are iscsi network disk type

Hi,

    For backing chain that all images are iscsi network disk type , such as
 iscsi://ip/iqn../0(base image) <-iscsi://ip/iqn../1(active image).
Currently,  'qemu-img info --backing-chain' command can display correct
backing file info, but after starting guest with the active image in
backing chain,  it don't include the related <backingStore> element in
dumpxml.

     So, Whether libvirt can support all backing chain layer are iscsi
network disk type?




Best Regards
Meina Li

On Wed, Jan 3, 2018 at 6:39 AM, Meina Li <meili@redhat.com> wrote:
> Hi,
>
> I am a libvirt qe, I am testing the function about the new location of
> disk auth element (as sub-element of the source element) in Backing Chain
> Management. And I have a questions:
>
> When all the backing chain are iscsi network disk type(no matter if the
> authentication is exist), start the guest ,  it will only has  the top
> level disk in xml and there are no other backingStore in it. The test step
> is below.
>
> So can this function support all backing chain with network disk type
> actually, or only use network authentication as the base image for backing
> chain of file disk type?
>
> Can you help reviewing it? Thanks very much in advance!
>
> Test step:
> 1.  iSCSI server:
>   o- iscsi ............................................................
> ................................................ [Targets: 2]
>   | o- iqn.2003-01.org.linux-iscsi.localhost.x8664:sn.9cba196611e6
> ....................................................... [TPGs: 1]
>   | | o- tpg1
.....................................................................................
> [gen-acls, tpg-auth, 1-way auth]
>   | |   o- acls ..............................
>
............................................................................
> [ACLs: 0]
>   | |   o- luns ..............................
>
............................................................................
> [LUNs: 4]
>   | |   | o- lun0 ..............................
> .................................. [fileio/file1 (/tmp/lun1.img)
> (default_tg_pt_gp)]
>   | |   o- portals ..............................
> ......................................................................
> [Portals: 1]
>   | |     o- 0.0.0.0:3260 ..............................
> .......................................................................
> [OK]
>   | o- iqn.2003-01.org.linux-iscsi.localhost.x8664:sn.a8d92ebb4ece
> ....................................................... [TPGs: 1]
>   |   o- tpg1 ............................................................
> ...................................... [gen-acls, no-auth]
>   |     o- acls ..............................
>
............................................................................
> [ACLs: 0]
>   |     o- luns ..............................
>
............................................................................
> [LUNs: 3]
>   |     | o- lun0 ..............................
> .................................. [fileio/file3 (/tmp/lun3.img)
> (default_tg_pt_gp)]
>   |     o- portals ..............................
> ......................................................................
> [Portals: 1]
>   |       o- 0.0.0.0:3260 ..............................
> .......................................................................
> [OK]
>
> 2. Set iscsi secret.
> # cat iscsi-secret.xml
> <secret ephemeral='no' private='yes'>
> <description>iSCSI secret</description>
> <usage type='iscsi'>
> <target>libvirtiscsi</target>
> </usage>
> </secret>
> # virsh secret-define iscsi-secret.xml
> Secret 47bd2f3e-023f-44ba-85a3-e8fa7f16ff23 created
> # MYSECRET=`printf %s "redhat" | base64`
> # virsh secret-set-value 47bd2f3e-023f-44ba-85a3-e8fa7f16ff23 $MYSECRET
> Secret value set
>
> 3. Create backing chain.
> # qemu-img create -f qcow2 -b iscsi://redhat:redhat@10.66.7.
> 27:3260/iqn.2003-01.org.linux-iscsi.localhost.x8664:sn.9cba196611e6/0
> iscsi://10.66.7.27:3260/iqn.2003-01.org.linux-iscsi.localhost.x8664:sn.
> a8d92ebb4ece/0 -o backing_fmt=qcow2
>
> 4. Start guest.
> # qemu-img info iscsi://10.66.7.27:3260/iqn.2003-01.org.linux-iscsi.
> localhost.x8664:sn.a8d92ebb4ece/0 --backing-chainimage:
json:{"driver":
> "qcow2", "file": {"lun": "0",
"portal": "10.66.7.27:3260", "driver":
> "iscsi", "transport": "tcp",
"target": "iqn.2003-01.org.linux-iscsi.
> localhost.x8664:sn.a8d92ebb4ece"}}
> file format: qcow2
> virtual size: 5.0G (5368709120 <0536%20870%209120> bytes)
> disk size: unavailable
> cluster_size: 65536
> backing file: iscsi://redhat:redhat@10.66.7.27:3260/iqn.2003-01.org.linux-
> iscsi.localhost.x8664:sn.9cba196611e6/0
> backing file format: qcow2
> Format specific information:
>     compat: 1.1
>     lazy refcounts: false
>     refcount bits: 16
>     corrupt: false
>
> image: json:{"driver": "qcow2", "file":
{"lun": "0", "portal": "
> 10.66.7.27:3260", "driver": "iscsi",
"transport": "tcp", "user":
> "redhat", "password": "redhat",
"target": "iqn.2003-01.org.linux-iscsi.
> localhost.x8664:sn.9cba196611e6"}}
> file format: qcow2
> virtual size: 5.0G (5368709120 <0536%20870%209120> bytes)
> disk size: unavailable
> cluster_size: 65536
> Format specific information:
>     compat: 1.1
>     lazy refcounts: false
>     refcount bits: 16
>     corrupt: false
>
> # virsh dumpxml rhel7 | grep disk -A 9
> ...
>     <disk type='network' device='disk'>
>       <driver name='qemu' type='qcow2'/>
>       <source protocol='iscsi' name='iqn.2003-01.org.linux-
> iscsi.localhost.x8664:sn.a8d92ebb4ece/0'>
>         <host name='10.66.7.27' port='3260'/>
>       </source>
>       <target dev='vdb' bus='virtio'/>
>       <alias name='virtio-disk1'/>
>       <address type='pci' domain='0x0000'
bus='0x00' slot='0x09'
> function='0x0'/>
>     </disk>
> ...
>
>
> Best Regards
> Meina Li
>

On Tue, Jan 09, 2018 at 22:12:00 -0500, Meina Li wrote:
> Hi,
> 
>     For backing chain that all images are iscsi network disk type , such as
>  iscsi://ip/iqn../0(base image) <-iscsi://ip/iqn../1(active image).
> Currently,  'qemu-img info --backing-chain' command can display
correct
> backing file info, but after starting guest with the active image in
> backing chain,  it don't include the related <backingStore>
element in
> dumpxml.
> 
>      So, Whether libvirt can support all backing chain layer are iscsi
> network disk type?
Libvirt can't introspect the backing chain for certain storage
technologies, thus the <backingStore> elements are missing for them.

Note that the chain should show up as unterminated (not having
<backingStore/> in the last visible layer) which indicates that there
may be images libvirt can't inspect.

This will eventually be solved by keeping the full backing chain in the
XML.